Recent advance in autoimmunity research reveals that the complement system is able to recognize self targets and initiates inflammatory response in a similar way as with pathogens. This application focuses on one such example of "innate autoimmunity", renal ischemia reperfusion injury (IRI). The long term goal of this project is to elucidate the pathways by which complement is activated in renal IRI, to determine the complement mediators responsible, define the downstream events of complement activation, and test the therapeutic efficacies of selective complement inhibitors in renal IRI. These studies will use mice globally or tissue-specifically deficient in the membrane complement regulatory proteins DAF, CD59 and Crry. Our specific aims are: 1) to determine if mice conditionally deficient in Crry (on renal tubules or on endothelial cells) will sustain tubular or glomerular injury either spontaneously or in response to IR challenge. We have developed a Crry gene floxed mouse and will cross this mouse with Aquaporin 2-Cre and Tie-2 Cre transgenic mice to generate tissue-specific Crry gene knockout mice. 2) to determine the pathways by which complement is activated during renal IRI in DAF-/-/CD59-/- mice and characterize the pathogenic natural antibodies and antigens involved. We will cross the DAF-/-/CD59-/- mouse with C4-/-, Ig-/-, C1q-/-, MBL-A-/- &C-/-, fD-/- and properdin-/- mice to achieve this specific aim. 3) to identify the responsible complement mediators and characterize the downstream events leading to renal IRI in DAF-/-/CD59-/- mice. We will use genetic and pharmacologic approaches to evaluate the roles of C3a, C5, C5a, macrophages, neutrophils, eicosanoids and cytokines in renal IRI. 4) to test the therapeutic efficacy of recombinant CR2-Crry and Compstatin, as a local and systemic C3 inhibitor, respectively, in renal IRI. These studies will increase our understanding of the role and mechanism of action of complement in "innate autoimmunity" and facilitate the development of anti-complement therapies in renal ischemia reperfusion injury, a major cause of acute renal failure in human patients.